I've come to the conclusion that the "oiliness" I've mentioned before is cause by dA/JPEG + browser. I've seen it in my on uploads as well. It gets worse as the structure in the image gets more fine-grained (that's why it's more apparent with shiny metal than with rust). I find it really annoying, because if I download any of my images and open them in a proper viewer it's gone. In other words: something is lost, and if that "something" forms a significant part of what's interesting to look at, that's bad.
I just noticed it can't be JPEG because my resized images are PNGs. But I've only noticed it since about 6 weeks ago. Do you run Firefox? They've changed some things wrt image rendering recently.
I think it's FF, I just started a Windows for a change (and glad to shut it down again) and in IE it looked crystal clear, especially the flaky paint bits. I noticed the FF people have caused images to be centered when doing the View Image thing, and software humans rarely do one thing at a time, so they might as well have been meddling with the rendering as such.